1. Field of the Invention
The present invention relates to a flaky, fine powder which is used as a mixing or compounding agent for cosmetics, pigments and paints, or as a filler for use with such materials as plastics, and production thereof. Furthermore, the present invention relates to cosmetics in which the aforesaid flaky, fine powder is mixed or compounded.
2. Description of Related Art
A flaky, fine powder has been used as a compounding agent for such materials as cosmetics, pigments and paints, or as a filler for such materials as plastics, and this type of flaky, fine powder, produced by covering the surface of a flaky substance such as mica as a base with metal oxide or other appropriate material is well known.
This type of flaky, fine powder is produced by precipitating hydroxide from aqueous solution of metallic salt under coexistence with a flaky substance as a base and depositing said hydroxide on the surface of the flaky substance.
However, a covering layer formed on the surface of the aforesaid flaky substance is a layer comprising primary particles and/or aggregated particles of the hydroxide and having an uneven thickness. For this reason, it is extremely difficult to control the form or thickness of the covered particles.
In addition, a main purpose of reduction of the conventional type of flaky, fine powder covered with oxides was to make use of the physical characteristics specific to the oxides used for covering the surface (such as a refractive index or a light transmittance), but a flaky, fine powder for use of its function originating from the shape of the covered particles has not been known.
In the German Patent Laid Open Publication No. 3922178 which was laid open on Jan. 17, 1991 after the priority date (Aug. 16, 1990) of the present PCT application, a minute flaky base which does not aggregate but has a high dispersibility, characterized in that said base contains spherical particles, each having a smaller diameter as compared to that of the minute flaky base, by at least 0.5% by weight, is disclosed. It is described in this publication that the minute flaky base having a diameter in a maximum range from 1 to 500 μm is suited, and that a diameter of the spherical particle should preferably be in the range from 0.05 to 50 μm.
It seems that the base can be easily moved because spherical particles act as a kind of ball bearing on the surface of the minute flaky substance.
Furthermore, in the aforesaid publication, the method of mixing a suspension of minute flaky base with a suspension of spherical particles, each having a smaller diameter as compared to that of the base, then filtering, drying, and calcining, if necessary, the base, is disclosed as the method of producing the aforesaid minute flaky base which does not aggregate and has a high dispersibility. Also, it is described in the publication that, when preparing the mixture described above, it is important to fully mix the two suspensions by means of ultrasonic processing.